If left untreated, over extrusion can also eventually lead to 3D printer nozzle jams. Over extrusion is a common problem in FDM 3D printing that can have a negative impact on the structural integrity and quality of your prints. Such calculated extrusion with is capped to max value equal to nozzle_diameter * 1.7, except for internal sparse infill where the full native flow is used.If your 3D prints are coming off the print bed with oozing or drooping layers, blobs, or signs of stringing, there is a good chance you are dealing with over extrusion. The purpose of this logic is to find the "native" flow that minimizes side forces during extrusion. In other words, by matching flow speed and head speed. A thin extrusion width provides better accuracy to the object shape and minimizes the flow errors caused by irregular filament.Įxtrusion width for other things is calculated by getting the cross-sectional area of the configured nozzle diameter and then calculating the extrusion width produced by extruding that amount of material. This is considered the thinnest safe extrusion width. Slic3r allows users to define extrusion width manually for each kind of extrusion (perimeters, infill, support material etc.) but will calculate sane defaults if no custom values are entered.įor the outermost loop of perimeters (aka external perimeters) Slic3r will default to a thin extrusion width, equal to nozzle diameter * 1.05. Spacing = extrusion_width - layer_height * (1 - PI/4) Sane defaults A value of 1 is currently being used to guarantee that the error (which is always present) is fully on the side of abundant extrusion rather than lacking material. In the past, several values were tried for overlap_factor, but some users were still reporting too sparse paths. It's difficult to estimate this amount, since it probably depends also on viscosity of plastic, extrusion speed and temperature. overlap_factor represents how much void remains between the extrusions. The ideal overlap would be something like: However, it's very unlikely that the second extrusion will fill the space below the previous one, so there would still be a little void. Ideally, we would want to fill all of that yellow area by placing the extrusions closed to each other. Void_area = layer_height^2 - (layer_height/2)^2 * PI The cross-section area of such voids is generally: So the relationship between desired extrusion width and volume to extrude is the following: Slic3r assumes that the cross-sectional shape of an extrusion is a rectangle with semicircular ends. In this case the problem is: what shape will our extrusion get? We know it will get squashed horizontally, but will it have a rectangular or oval shape? What's the maximum extrusion width we can get with a given nozzle diameter before plastic starts curling at the sides? The required material volume for a path of unitary length is calculated accordingly to the cylindric shape, thus with a circular cross-sectional area: E = (nozzle_diameter/2)^2 * PI Extruding on top of a surface (In case of bridges, we want no overlap because it has proven to drag the existing paths.) Parallel paths will be positioned so that they are tangent, thus the spacing between one path and its neighbor is equal to nozzle diameter as well. Extrusions are round and their diameter is equal to the nozzle diameter. Bridges: the easy caseĪs said above, there's only one correct flow rate for bridging: the one that doesn't make your bridge sag or break. It's not the distance of two adjacent paths since some overlap will be generally applied in order to get better bonding. If, on the contrary, you extrude too much material, the shape of the extruded filament won't change (still equal to nozzle diameter) but you'll get a loose bridge.Įxtrusion Width is the thickness of a single filament extruded either in free air or above a surface. Actually, if you reduce the material flow you'll get smaller circles to some extent, until the plastic viscosity decides it's time to break your bridge because of too much tension.
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